For the purposes of hemostasis upon incision of an affected area, blocking of the nutrient supply to a tumor, maintenance of the concentration of an anticancer drug in a tumor, and the like, a poly(lactic acid/glycolic acid) copolymer (JP 5-969 A), a block copolymer of polyethylene glycol and polylactic acid (JP 5-17245 B, JP 2004-167229 A, JP 2005-312623 A and JP 2007-291323 A), or a multiblock copolymer obtained by copolymerizing lactic acid, polyethylene glycol, polyvalent carboxylic acid and the like (US Publication No. 2009/0117033) is used as polymer particles for embolization of blood vessels and the like.
Such polymer particles for embolization of blood vessels and the like are used in the shape of spherical particles to tightly and securely embolize the blood vessels and the like. However, since the particles are delivered to the target site such as a blood vessel through a microcatheter or the like, the particles have problems such as insufficient flexibility of the particles themselves, occurrence of aggregation to cause clogging of the catheter, and irreversible deformation of the polymer particles before they reach the target site.
To solve these problems, attempts have been made, for example, by covering the surface of the polymer particles with polyethylene glycol to prevent their aggregation and hence to increase their ability to pass through a catheter (JP 2007-145826 A), by blending a plurality of types of polymers to control flexibility of the polymer particles (JP 2007-146146 A), or by developing a chemically cross-linked polymer particle (JP 2005-314535 A).
However, although an increase in the ability to pass through a catheter and improvement in controlling flexibility of the polymer particles can be seen in the improved techniques such as covering of the surface of polymer particles (JP 2007-145826 A), blending of a plurality of types of polymers (JP 2007-146146 A) and use of chemically cross-linked polymer particles (JP 2005-314535 A), in sufficient improvement can be seen in terms of the problem of irreversible deformation of polymer particles. Hence, further improvement has been required to obtain a good embolization action for blood vessels and the like. That is, development of an embolization material for blood vessels and the like wherein the ability of the polymer particles to recover their original shape after passing through a catheter (hereinafter referred to as “particle shape-recovering ability”) is enhanced has been demanded.
In view of this, it could be helpful to provide a biodegradable vascular embolization material that is less likely to coagulate and has an improved flexibility, and whose particle shape is recovered after its passing through a catheter or the like.